"From a societal perspective, I would say that old people are young people later in life," said Dr. Stacy Tesler Lindau, lead author of the federally funded study, which was published in the New England Journal of Medicine.

Sexual activity reported among the 3,005 men and women who participated in the survey did decrease with age, particularly among the oldest participants -- from 73 percent among those 57 to 64 years of age to 53 percent among those 65 to 74 years of age to 26 percent among those 75 to 85 years of age.

Discussion of the sex habits of American seniors has received little attention, even from scientists.

"Hopefully, this opens the door for conversation that might counter stereotypes," Lindau told reporters in a conference call. "If we regard older people as asexual, particularly as physicians, we really miss an opportunity to do important counseling and interventions for people who may benefit from them."

Among the survey's many discoveries was that about half of those 57 to 75 years of age who remained sexually active reported engaging in oral sex.

More than half of men and a quarter of women said they had masturbated during the previous year, a figure that remained constant whether they were sexually active or not.

The figure on masturbation "reflects a level of sexual need, even among men at very advanced ages, and speaks to the fact that sexuality is a lifelong proposition," said Edward O. Laumann, a study co-author and a sociologist at the University of Chicago.

But not for everybody. Thirty-five percent of women versus 13 percent of men rated sex as "not at all important."

Sex and Seniors

 Sex with a partner in the previous year was reported by 73 percent of people ages 57 to 64; 53 percent of those ages 64 to 75, and 26 percent of people 75 to 85. Of those who were active, most said they had sex two to three times a month or more.

 Women at all ages were less likely to be sexually active than men. But they also lacked partners; far more were widowed.

 People whose health was excellent or very good were nearly twice as likely to be sexually active as those in poor or fair health.

 Half of people having sex reported at least one related problem. Most common in men was erection trouble (37 percent); in women, low desire (43 percent), vaginal dryness (39 percent) and inability to have an orgasm (34 percent).

 One out of seven men used Viagra or other substances to improve sex.

 Twenty-two percent of women and 38 percent of men had discussed sex with a doctor since age 50.

That sentiment increased with age: 41 percent of the oldest age group said they felt that way, versus 25 percent of the middle group and 15 percent of the youngest group.

Across all age groups, women were less likely than men to report having engaged in sexual activity during the previous year. The disparity was attributed to the fact that women typically outlive men. Though 78 percent of men ages 75 to 85 had a spouse or other intimate relationship, the figure for women of the same age range was 40 percent.

Among those who said they were sexually active, about half of men and women reported at least one sexual problem that bothered them, including low desire (43 percent), difficulty with vaginal lubrication (39 percent) and inability to climax (34 percent).

The most common problem reported by men was difficulty gaining or maintaining an erection (37 percent).

About one in seven men (14 percent) said they were using drugs to improve their performance.

About one in four sexually active adults with a sexual problem said it led them to avoid sex.

Despite the high prevalence of sexual problems, few respondents -- 38 percent of men and 22 percent of women -- said they had discussed them with their doctors.

"Most felt sexuality is an important part of life, but feel physicians need to initiate discussion" about it, Lindau said.

Only a small minority -- 3.5 percent for men and 1.5 percent for women -- said they had had more than one sex partner during the previous year. Though the authors asked about prostitution, they said they had not yet reviewed those data.

Study author: 'Data are a gold mine'

The survey elicited an unusually high response rate of about 75 percent. Participants were paid $100 to submit to a two-hour interview and half-hour physical exam about a topic that has rarely been studied in detail, the authors said.

"These data are a gold mine," said co-author Linda Waite, a sociologist at the University of Chicago, and will be particularly useful to baby boomers about to become seniors.

But the study had limitations: Only sexually active individuals were asked about problems, meaning the findings likely underestimate the true incidence of sexual problems.

And much of the data were self-reported, meaning the results assume the subjects were truthful.

That may not always have been the case: The study found eight people who said their sex partner was of the same gender, a figure lower than commonly accepted estimates and one that Laumann acknowledged raises questions about the veracity of the respondents.

"I think you have to ask these questions, and I think they are very valid worries," Laumann said.

In an accompanying editorial, Dr. John H.J. Bancroft, the former director of the Kinsey Institute for Research in Sex, Gender and Reproduction, noted the survey gave little attention to those who said they were sexually inactive.

"Unfortunately, the present study did not assess the proportion of respondents in a relationship who had become sexually inactive because of sexual problems, whether men or women had these sexual problems, and how the respondents felt about their relationship," he said.

Laumann responded that the survey was able to cover only so much material. "It's a question of what you can cover in the amount of time we had," he said.E-mail to a friend